10 GEOLOGY. 
shore of San Pablo bay, the association of the shales and sandstones of San Francisco with 
a series of fossiliferous and infusorial strata of great thickness. During my recent visit, 
in an examination of the coast line south of Point Lobos, I discovered strata of white infusorial 
rock and beds of lignite in still more immediate proximity to the strata underlying San Fran- 
cisco, and, torn up by the surf, masses of a shell conglomerate, in which are imbedded large 
numbers of Scutella interlineata. Following down the coast, we observed the same, or a similar 
geological series, exposed at a thousand different points where the waves of the Pacific had eaten 
deeply into the bases of the Coast mountains. This series has suffered great displacement and 
considerable metamorphosis through the proximity or protrusion of igneous rocks along the 
many lines of uplift marking the spurs and parallel ranges of the Coast mountains. 
At San Luis Obispo the disturbance of the Tertiary series is particularly marked. The pre- 
vailing rocks at this point are fine argillaceous, probably infusorial, shales, sandstones, and 
shell conglomerates. Many of these strata are highly charged with bitumen, which is caused 
to exude by the sun’s heat, and drips down from the cliffs, forming masses of considerable size 
and of great purity. Of these strata the shales to which I have referred are much disturbed; 
in places standing quite vertical, and in some instances are so highly metamorphosed as to 
become almost vitreous, resembling a fine white or light gray porcelain. 
At various points between Monterey and San Diego the bituminous exudations form a feature 
so striking as to attract the attention and excite the curiosity of all who visit that region, whether 
learned or unlearned; but, as yet, no satisfactory theory has been advanced to account for 
their existence. From the fact, however, that beds of lignite are so characteristic of the 
geology of the Coast mountains, and are inseparably associated with the Miocene strata from 
Bellingham bay to San Diego, it seems to me the most simple explanation of the existence of 
these bituminous exudations to refer their origin to that source. It is true that exposures of 
strata of lignite are not frequently observable in the region where the asphaltum is most 
abundant; but they exist even as far south as San Diego, as is proved by the borings made 
near Point Loma, where operations have been commenced for reaching the coal by shafts. 
The district marked by these bituminous springs and accumulations has suffered a greater 
amount of volcanic disturbance than any other portion of the coast; and while the application 
of volcanic heat to beds of lignite would produce precisely similar results, by driving off the 
bituminous matter which they contain, we can hardly imagine any other adequate cause for the 
phenomena. The deposits of bitumen of Trinidad and Cuba, which closely resemble those of 
. the Pacific coast, have been, I believe, uniformly considered by those who have studied them 
most carefully, to be the result of a similar process. The objection to this theory which has 
been advanced, derived from the absence of lignites from the sedimentary series at some points 
where the contact with the underlying igneous recks has been observed, is hardly conclusive; 
for we know that the lignite beds are by no means*continuous, but are far more local than the 
coal strata of the carboniferous series, and are probably the results of a somewhat different 
rocess. e coal seams were formed from plants which grew on the spot where their remains 
are found; but the Tertiary lignites of the Pacific coast have in many cases been derived from 
transported materials. My examination of the strata in the vicinity of San Luis Obispo led 
me to suspect that the asphaltum had been driven up by volcanic heat, and had thus impreg- 
nated the more porous strata for a long distance from its point of origin. 
The labors of the geologists to whom I have referred have clearly proven the general identity 
of structure of the Coast mountains throughout Southern California ; and yet many questions 
of interest remain to be settled in reference to the connexion between the Coast mountains, 
properly so called, and the Sierra Nevada. The ranges of this latter system, as we approach 
the southern boundary of the State, come constantly nearer the ocean till one of its great sub- 
divisions usurps the place of the ranges forming the coast line northward, and in the peninsula 
of Lower-California becomes itself the boundary between the ocean and the continent. From 
om 
Se 
